1. Field of the Invention
This invention relates to a dampening mechanism for offset rotary printing presses with a supply roller partly immersed in the dampening fluid, with downstream rollers transferring the dampening fluid to the printing plate, and with an elastic metering means which cooperates with the supply roller.
One type of dampening mechanism is described in German Patent No. 20 54 678 and a corresponding U.S. Pat. No. 3,744,414, in which there is a supply roller with a metering roller to meter the quantity of dampening fluid to be transferred to the printing plate. Such metering rollers are provided with an elastic jacket surface and are placed in contact with the supply roller by means of adjustable cams to squeeze off and thereby reduce the amount of dampening fluid thereon.
These characteristics have been controlled on metering rollers of the prior art, as far as possible, by means of separate, adjustable or variable drives to guarantee an even supply of dampening fluid, even at different printing speeds. However, the apparatus required for the controls, drives and circuitry significantly increases the cost of the dampening mechanism.
German Patent No. 15 61 113 includes a dampening mechanism which appears to employ a feed or supply roller for the introduction of dampening fluid to the printing plate thereof. A first squeeze or metering roller basically removes excess dampening fluid from the feed or supply roller. However, an additional pair of squeeze rollers are located at the ends of the feed or supply roller for alternative removal of additional dampening fluid when relatively narrow paper is employed. The two squeeze or metering rollers at the ends of the supply roller are therefore capable of removing dampening fluid which might accumulate on the inking rollers if not properly removed during the printing process. There is even disclosure of the alternative use of blower apparatus in this region to ensure adequate removal of dampening fluid at the edges of the supply roller.
German Patent Nos. 15 61 113 and 20 54 673 and U.S. Pat. No. 3,744,414 are incorporated by reference as if included in their entirety herein.